Maintaining gut health is important for the production of high quality and profitable poultry. The goal of this study was to examine the effects of supplemental mannan oligosaccharide (Bio-MOS (R)), Vitamin E (VE) and C (VC) on the growth performance and immune response of broilers given a corn based diet over a 6 weeks experimental period. About 1 day old male broilers (n=300) were randomly distributed to 4 groups (75 birds in each group and 15 birds in each subgroup for repetation 5 times) and reared under similar conditions. Standard husbandry and good management practices were followed that met or exceeded industry guideline. At each feeding, the following treatments were administered: control (no Bio-MOS (R), VE and VC), 1.5 g kg(-1) Bio-MOS (R), 500 mu g kg(-1) VE and 500 mu g kg(-1) VC. Body Weights (BW), Feed Intake (FI) and Feed Conversion Ratio (FCR) were measured on day 1, 21 and 42. Blood samples were taken from vena ulnaris every 7 days and were analyzed on IgG concentration. The results showed that there was no significant difference in BW, FI and FCR among the treatment groups. During the 6 weeks of trial period considering plasma IgG levels significant differences were only found as following: compared to control group it was significantly lower in VE group at week 1 and 2, higher in VC and Bip-MOS (R) groups at week 2 and lower in Bio-MOS (R) group at week 6. Additionally, at 4 week lowest (0.90+/-0.06 mg, n=15) and at 5 week highest (2.85+/-0.18 mg, n=15) plasma IgG levels was found after applying the dietary treatment in Bio-Mos (R) group. Consequently, this data suggest that supplementation of Bio-MOS (R), VE or VC may not improve either broiler performance or immune response in healthy broilers.